You may have read conflicting opinions in the news lately about tests that screen for early signs of cancer. Should you be tested for cancer even if you have no symptoms? Where can you find trusted information to help you decide?

The Norris Cotton Cancer Center is one of 41 institutions that the National Cancer Institute (NCI) has designated as a comprehensive cancer center. The NCI recently interviewed Dr. Barry Kramer, former associate director of the Office of Disease Prevention at the National Institute of Health, about the benefits and harms associated with cancer screenings

Should I be screened for cancer?

"There are several cancers that have been shown to be successfully screened with a net benefit compared to harm," Kramer said, citing pap smears for cervical cancer, fecal blood tests for colorectal cancer, and mammography for breast cancer. But he noted that all screening tests have some down sides. "It's always best to be informed when you are dealing with a medical procedure that has potential harms," he said.

Weigh cancer screening benefits against possible harms

The best approach is to make an informed decision: learn about the harms associated with a screening test, see if it has been proven to decrease the risk of dying from cancer, and talk with your doctor about whether the benefits outweigh the risks for you.

"What do people need to know to make good decisions?" Steven Woloshin, MD,MS asked at a NCCC grand rounds presentation, Know your Chances: Making Sense of Cancer Risks. "They need the facts, they need to know their options, they need to know the likely outcomes of their options, and to have some clarity of their values: how much do they care about the different outcomes?"

Which cancer screening tests are most effective?

There isn't a simple answer. Some tests are only recommended for those who are at high risk because the effectiveness of the test hasn't been proven or the test can't detect the disease at a curable stage. Some screenings are effective only in certain situations.

For example, it is known that regular Pap test screening of women between the ages of 25 and 60 years decreases their chance of dying from cervical cancer. But the benefits and harms of screening for breast cancer change with age, or for groups with different risk factors. NCI's Breast Cancer Risk Assessment Tool estimates a woman's risk for breast cancer during the next five years and up to age 90. If you have risk factors for breast cancer, you might want to talk to your doctor about when to begin having mammograms and how often to be screened.

And while screening for lung cancer with chest x-rays or sputum cytology does not decrease the risk of dying from lung cancer, screening with low-dose spiral CT scans has been shown to decrease the risk of dying from lung cancer in heavy smokers.

What are the benefits of preventive screening?

For some cancers, early detection often leads to more effective treatment and lowered risks:

Pap smears have led to the reduction in deaths from cervical cancer worldwide.

Fecal occult blood tests (FOBTs) have been found to decrease the risk of dying from colorectal cancer, the second leading cause of cancer deaths in the United States.

Mammograms have been established as an effective test for detecting breast cancer, which is the second leading cause of death from cancer in American women.

What are possible harms associated with preventive screenings?

Overdiagnosis: Early detection of some cancers does not improve the chance of a cure or help a person live longer.